Emitters that transmit radio frequency (RF) electromagnetic radiation can take the form of many known devices. For example, mobile telephones, 2-way radios, surveillance electronics and RF tags all transmit RF electromagnetic radiation to communicate with a receiver.
Locating emitters is important for safety, emergency, security and inventory control reasons. For example, if a criminal is using a mobile telephone, pinpointing his location will assist the police in capturing him. In an emergency, locating a person transmitting a signal is important for rescuing him. For security, locating and eliminating surveillance electronics will insure that confidential discussions remain confidential. RF tags can be used for inventory control or locating products in a large warehouse that are have such tags attached to them.
One known technique for locating an emitter employs a directional antenna to identify the direction of the emitter source. Limitations to this technique are that the directional antenna must be physically moved about to identify the direction of the emitter source, multipath and large path loss variation can cause erroneous readings and no information is provided regarding the range to the unknown source.
Another known technique for locating an emitter employs a plurality of base stations. Each base station receives the emitter signal and measures the direction of arrival (DOA). The emitter location is then determined by triangulation based on the DOA. While this technique is fairly accurate, it still suffers from multipath and large path loss variation and it requires a significant hardware deployment of many base stations.
A goal of the invention is to overcome the identified limitations and to provide an efficient and cost effective apparatus and method for emitter location.